(1) Field of the Invention
The invention concerns a blade rotary assembly including an aerodynamic outer toroid spoiler, a shrouded propulsion rotary assembly and a vehicle.
(2) Description of Related Art
The most general technical domain of the invention is the domain of propulsion rotor assemblies, for creating airflows by rotating blades (i.e. airfoil designs providing a “fan like” effect). In short, such shrouded propulsion rotary assemblies include mainly a driven rotor system including the blades, and a stator hollow structure.
The stator hollow structure include a hollow duct defining an inside vessel surface. The driven rotor system is functionally mounted inside the hollow duct. Each blade has an inner shank (root) radially opposed to an outer tip, mechanically coupled to a central hub of the driven rotor system. Each blade also has an outer tip. Being motorized/mechanically driven by a motion source, blades in the driven rotor system are rotated when required, for creating airflows.
In most shrouded propulsion rotary assemblies, the outer tips of the blades are generally free ended (not being linked to other tips). Such outer tips are distant/separated from neighboring outer tips by an angular free spacing. Such outer tips are also remote from the inside vessel surface of the stator hollow structure by a radial air spacing. Other way speaking, in most shrouded propulsion rotary assemblies, only the inner shanks of the blades are mechanically coupled to the central hub.
During operation, the free outer tips of the blades withstand considerable efforts, and provoke deleterious stresses, turbulences and noise.
In traditional helicopters, a main rotor is having an upright rotational axis for forward movement/hovering of the aircraft and an open-type tail rotor having a transverse axis. Together with direction controlling actions, such open-type tail rotor is providing compensation of the torque reaction of the main rotor.
More and more, these open-type tail rotor have been replaced by shrouded (i.e. ducted) propulsion rotary assemblies, in order to reduce noise, to enhance direction controlling, and to increase the security as well as the reliability from failure. Inspired from the basic concept of a shrouded/ducted fan, many types of shrouded propulsion rotary assemblies for helicopter tails have been proposed.
For preparing the instant application, the following prior art documents were considered: DE19752369, FR2534222, U.S. Pat. No. 4,585,391, U.S. Pat. No. 4,809,031, U.S. Pat. No. 4,911,612, U.S. Pat. No. 4,927,331, U.S. Pat. No. 5,102,068, U.S. Pat. No. 5,131,604, U.S. Pat. No. 5,306,119, U.S. Pat. No. 5,542,818, U.S. Pat. No. 5,588,618, U.S. Pat. No. 5,634,611, U.S. Pat. No. 6,736,600, U.S. Pat. No. 8,061,962, U.S. Pat. No. 7,959,105, US2011/0217163.
Teaching of the prior art is sometimes antagonistic. For instance, were proposed in the prior art related to tail arranged shrouded propulsion rotary assemblies:                to increase thrust, a rotating hub may have a radius of about 40% that of the tunnel. A helicopter equipped with a directional and stabilizing device having a faired and slanted anti torque rotor and a dissymmetric <<V>>;        to enhance the conditions encountered towards the end of the blade, are provided evolutions of curvature in some regions avoid shock wave. The evolutions of curvature in some regions towards the end of the blade ensure a progressive recompression of the flow. The evolutions of curvature in some regions towards the end of the blade ensure a decreasing in intensity in the vicinity of the trailing edge. And recompression avoids a premature separation of the boundary layer. This is giving low values of coefficient of drag for high coefficients of lift towards the end of the blade;        to minimize pressure losses across the blades by a small clearance (of about 2.5 mm) between the tips of the blades and the surface of the airflow duct, with a magnitude of the clearance dimension versus the overall fan assembly diameter to about 1 m for most purposes;        to reduce the noise from the tail rotor, the tip speed is reduced and the rotor blades are arranged at unequal angular intervals;        to provide rotor blades with swinging pitch horns, and to change a pitch angle of respective rotor blades. To have a first type of rotor blades having a larger mounting angle to obtain a predetermined thrust and a second type of rotor blades at a smaller mounting angle;        to have an air flow rectifying stator is located in the channel after the rotor blades and lying at an angle to the radial direction and inclined in the opposite direction to the rotor blades.        
The blades of the rotor which can rotate in the transverse duct have an angular distribution according to an uneven azimuth modulation given by the following sinusoidal law.
In a helicopter with mid-sized mass, the counter-torque rotor have blades driven with a given peripheral blade tip speed in a duct of about 1.1 meter in diameter. A flow straightening arrangement comprises vanes, mostly profiled ones with a given chord and to which the transmission arm is added. Thus is applied a distorted sinusoidal law in order to obtain phase modulation leading to no angle between two arbitrary blades, equal to any angle between two arbitrary vanes.
For minimizing the noise emitted by a ducted tail rotor anti-torque device at a frequency and perceived at another frequency, the diameter, the number of blades and the tangential speed of the rotor are determined so that the perceived frequency is less than or equal to the bottom limit frequency of a predetermined one-third frequency octave centered on a third frequency.
Furthermore, for optimizing the complete blade, it is generally advantageous, from the standpoint of yield, to have, especially in the case of a shrouded propeller, a span wise distribution of lift, which increases from the hub up to the end of the blade. The end sections, for which the relative speed is highest, therefore also operate with the highest coefficients of lift of adaptation. It is known that the coefficient of lift of adaptation is the coefficient of lift at which the section must work with a minimum coefficient of drag and for which it is defined.
Additionally, it is known that, for the known sections, the increase in the speed and the coefficient of lift is translated by an increase in the coefficient of drag and this increase is faster as the Reynolds number is lower, which is the case for the applications envisaged by the present invention.
The use of known sections therefore leads to deleterious losses and the yield of a shrouded propeller presenting such a known section remains too low for some aircrafts.
The document U.S. Pat. No. 5,566,907 describes rigidly secured blades of a rotor which can rotate in a transverse duct and that have an angular distribution according to an uneven azimuth modulation given by a sinusoidal law: The angular position of the blades are counted in series from an arbitrary origin.
The document U.S. Pat. No. 7,959,105 describes an aircraft having a streamlined stator pierced by an air flow duct defined around an axis of symmetry. The aircraft has a shrouded rotor with rotary blades arranged in said static air flow duct. The periphery of the static air flow duct is provided in succession of a first lip, a second lip and of a first rear portion at the side of the duct that is closer to the rear end of the aircraft. The second lip has a second front portion situated at the side of the duct that is closer to the front of the aircraft. The aircraft is fitted with blower means for reducing the noise generated by the shrouded rotor and suitable for propelling compressed air towards a first injection zone opening out into the first rear front portion and to a second injection zone opening out to the second front portion, in the stator.
Despite of advantages provided, remains a need for a unit propelling compressed air towards the injection zone which in some way compensates the negative effects of the inlet flow separation at the leading side of the inlet lip for cross-wind air flows. However, this document, only showing rotary blades with free outer tips, does not solve the problems of hub corner separation and of lip clearance losses.
The document US2011/0217163 describes a double-ducted fan that includes a hub, a rotor having a plurality of blades with free outer tips. A stator first duct, a stator second duct, and a stator channel are defined. The first duct circumscribes the rotary free outer tips of the blades, and the second duct circumscribes the first duct. The channel is configured to direct air flow cross-wise to the first duct over a top of the first duct into the inlet side of the fan. The second duct is movable relative to the first duct to adjust a portion of the channel. The length of the first duct is different from the length of the second duct.
This document is especially applicable for isolated ducted fans but not for shrouded tail rotors. Tail rotors are different in that they have no outer wall of the shroud. Furthermore, this document does not solve the problem of lip clearance loss, since there is still a gap between the inner wall of the shroud and the rotor tips.
The document U.S. Pat. No. 5,102,068 describes a spiroid tipped wing. This spiroid-tipped wing, in its basic form, comprises a wing-like lifting surface and a spiroid tip device integrated so as to minimize the induced drag of the wing-spiroid combination and/or to alleviate noise effects associated with concentrated vortex effect wakes that trail from lifting surfaces. The ends of the spiroid are attached to the wing tip at appropriate sweep and included angles to form a continuous and closed extension of the wing surface.
For a fixed wing aircraft the spiroid configuration on the right side is of opposite hand to that on the left side. The spiroid geometry incorporates airfoil cross sections with specified thickness, camber and twist. The airfoil thickness varies in relation to the local sweep angle being a minimum at an intermediate position where the sweep angle is zero. The camber and twist vary approximately linearly and change sign at some intermediate position between the spiroid ends so as to produce the optimum spiroid loading. Increasing the size of the spiroid in relation to the overall span of the lifting surface is used to further reduce drag and noise. The concept of the spiroid-tipped wing may include the use of more than one spiroid on each wing tip in any number of forms which may be selected to be adaptable to other design requirements and operational limitations. More generally the spiroid wing tip system is a generic geometric concept which can be adapted to achieve drag reduction and noise for most applications which incorporate wings or wing-like devices (i.e. lifting surfaces) such as helicopters, propellers, etc. including non-aeronautical applications.
This document has the target to reduce the induced drag at the wing tips of ordinary wings of aircraft. Despite this technique could in theory be applied for reducing the lip clearance losses of ducted/shrouded tail rotors, the specific constructions which are proposed in the patent are difficult to realize. Furthermore, the invention would not provide solutions for inlet lip separation and for hub corner separation.
The document DE19752369 describes a drive body which is based on principles derived from the vortex flow of the wings of gliding birds. At its origin, or in wingspan direction from the wing root to the wing tip, the transverse drive creating structure is connected to a long base part (base wing) to provide overall an almost continuous distribution of the transverse drive at the transition point to two narrower transverse drive bodies which merge with each other without sharp bends.
The drive body is based on principles derived from the vortex flow of the wings of gliding birds. At its origin, or in wingspan direction from the wing root to the wing tip, the transverse drive creating structure is connected to a long base part (base wing) to provide overall an almost continuous distribution of the transverse drive at the transition point to two narrower transverse drive bodies which merge with each other without sharp bends.
This document is proposed in order to reduce the induced drag of wings of aircraft with a light-weight but mechanically stable construction. This concept has been developed for larger aircraft wings and does not seem to be helpful for the optimization of a shrouded anti-torque rotor.
The document U.S. Pat. No. 6,736,600 describes a rotor, which in operation is flown through by a fluid in a main flow direction, the rotor having a rotor blade arranged rotatable around a rotor axis and extending at least partially away from the rotor axis into the fluid. To reduce the trailed tip vortex at the end of the rotor blades, the fluidic losses, as well as the flow noise, the rotor blade is split into at least two partial blades at a predetermined distance from the rotor axis and forms a loop. One partial blade extends in the direction of rotation in relation to the rotor blade. The other partial blade extends in a direction opposite the direction of rotation to the rotor blade. The two partial blades are interconnected in one piece at their ends, to encompass a loop surface extending essentially crosswise to the main direction of flow, through which the fluid flows.
As per this document, the split of the rotor blade in two parts could be applied to shrouded tail rotors, in order to optimize the air flow through the shroud/duct.
Though, limits and drawbacks remains, despite the valuable enhancements brought to such tail arranged shrouded propulsion rotary assemblies.
However, there is still a need for further optimizations in order to increase the efficiency and further reduction of the noise. Such an increase of efficiency could make the ducted tail rotor an alternative also for larger helicopters which at the moment still need to rely on conventional tail rotors.